Annihilation Cross Sections for Relic Densities in the Low Velocity Limit
Abstract
A simple method to calculate the total annihilation cross section of massive cold relics is presented. Exact expressions for , , and of σ =+ 2+ 4 are obtained from simple derivatives of the squared annihilation amplitude. Three examples are given. In one example, the computed annihilation cross section of massive Dirac neutrinos confirms recent correct calculations.
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